Carbon dioxide and activity monitoring

ABSTRACT

An implanted heart monitor includes sensors that measure various aspects of the heart failure patient&#39;s heart. A remote heart monitoring system connects the implanted heart monitor to a care provider, such as a physician. The data provided by the implanted heart monitor permits the care provider to obtain valuable data on the heart in order to make health care decisions affecting the heart failure patient&#39;s treatment. In many cases, the measurement of core body temperature and other patient data will enable the care provider to alter the patient&#39;s treatment to address the patient&#39;s condition. The implanted heart monitor can communicate over a wireless communication link with an external monitor. The implanted heart monitor may be implemented as part of a pacing device (i.e., pace maker) or may be a separate unit devoted to monitoring functions. The external monitor communicates with a monitoring station over a communication link. The monitoring station can operate as a centralized data collection unit, collecting data from multiple external monitors and multiple implanted heart monitors. Various other aspects of a heart failure patient&#39;s heart and/or body can be monitored, such as heart rate, blood pH levels, blood CO 2  levels, and any other indications of the heart failure patient&#39;s activity. Various predetermined thresholds may be set to trigger alarms and/or data reports.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/258,432, filed Oct. 25, 2005, which is a divisional of U.S. patentapplication Ser. No. 10/154,142, filed May 22, 2002, now U.S. Pat. No.7,037,273, said applications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to monitoring heart performance in heartfailure patients. More specifically, the present invention relates tomonitoring heart performance to detect the occurrence of a drop in corebody temperature in heart failure patients.

BACKGROUND OF THE INVENTION

As early as 1985, medical literature documented a relationship betweendecreased core body temperature and increased bodily activity in heartfailure patients. In a paper by Stanley A. Rubin (RUBIN, STANLEY A. Corebody temperature regulation of heart rate during exercise in humans. J.Appl. Physiol. 62(5): 1997-2001, 1987), a significant correlation wasfound between an observed change in core body temperature and heart ratechanges in heart failure patients. Rubin defined core body temperatureas the mixed venous blood pool found in the pulmonary artery. Using athermistor mounted on the distal end of a Swan-Ganz catheter, Rubinfound that the core body temperature of heart failure patients decreasedduring exercise, while the core body temperature in normal patientstypically increased during exercise.

This relationship between core body temperature and heart activity hasbeen observed in other studies. In a paper by Frank G. Shellock, et al.(SHELLOCK, FRANK G., H. J. C. SWAN, AND STANLEY A. RUBIN. Muscle andfemoral vein temperatures during short term maximal exercise in heartfailure. J. Appl. Physiol. 58(2): 400-408, 1985), reductions in corebody temperatures in heart failure patients were observed while theheart failure patients underwent exercise. Shellock, et al. concludedthat the core body temperature decrease observed in heart failurepatients is partially caused by the re-distribution of cooler blood fromthe underperfused skeletal muscles into the core blood during exercise.Another paper by Shellock and Rubin (FRANK G. SHELLOCK AND STANLEY A.RUBIN. Mixed venous blood temperature response to exercise in heartfailure patients treated with short-term vasodilators. ClinicalPhysiology 5, 503-514, 1985), also concluded that the core bodytemperature drop was due to circulatory inadequacies. This conclusionwas based on Shellock's and Rubin's conclusion that heart failurepatients treated with vasodialators experience an attenuation of thecore body temperature response typical during exercise, as a result ofvasodialator-induced improvement in circulation.

More recent research ascribes the drop in core body temperature to lowblood pH levels. As a heart failure patient exercises, the heart failurepatient experiences an increase of CO₂ in its blood as the bloodattempts to eliminate the CO₂ from the exercising muscles. The heartfailure patient will normally increase its breathing volume in anattempt to evacuate the increased level of CO₂ from the blood. However,in heart failure patients, the blood system cannot deliver the blood tothe lungs fast enough to support an adequate CO₂ for O₂ exchange in thelungs. It is well known that higher levels of CO₂ correlate with lowerlevels of blood pH. As CO₂ accumulates in the heart failure patient'sbody, the blood's pH level drops. Because pH is a catalyst for virtuallyevery chemical reaction in the body, the heart failure patient'schemical reactions will be slowed by the reduced pH levels. As theblood's pH level drops with the increased CO₂ levels, the heart failurepatient's bodily chemical reactions responsible for heat productionduring exercise are slowed and the core body temperature stays flat ordecreases.

While the core body temperature drop phenomenon has been documented inthe literature described above, little has been done to apply thisknowledge to benefit heart failure patients. A heart failure patient mayrequire immediate medical attention or an alteration of medicaltreatment in certain conditions where an increase in heart activity anda decrease in core body temperature are coincident.

Therefore, there is a need in the art for a core body temperaturemonitoring system that can determine when the core body temperaturelevel of a heart failure patient is outside of an acceptable range. Themonitoring system also should determine whether the relationship betweenthe core body temperature level and the activity of the heart failurepatient is outside of an acceptable range. The monitoring system shouldbe capable of generating an alarm when an unacceptable level has beendetected. The monitoring system also should be able to transmit an alarmto a remote location.

SUMMARY OF THE INVENTION

An implanted heart monitor of the present invention includes sensorsthat measure various aspects of the heart failure patient's heart. Aremote heart monitoring system can connect the implanted heart monitorto a care provider, such as a physician. The data provided by theimplanted heart monitor permits the care provider to obtain valuabledata on the heart in order to make health care decisions affecting theheart failure patient's treatment. In many cases, the measurement ofcore body temperature and other patient data will enable the careprovider to alter the patient's treatment to address the patient'scondition. The implanted heart monitor can communicate over a wirelesscommunication link with an external monitor. The implanted heart monitormay be implemented as part of a pacing device (i.e., pace maker) or maybe a separate unit devoted to monitoring functions. The external monitorcommunicates with a monitoring station over a communication link. Themonitoring station can operate as a centralized data collection unit,collecting data from multiple external monitors and multiple implantedheart monitors. Various other aspects of a heart failure patient's heartand/or body can be monitored, such as heart rate, blood pH levels, bloodCO₂ levels, and any other indications of the heart failure patient'sactivity. Various predetermined thresholds may be set to trigger alarmsand/or data reports.

In one aspect of the present invention, a heart monitoring system isprovided. The heart monitoring system includes a temperature sensor fordetermining a core body temperature of a patient and a bodily activitysensor for determining a bodily activity level of the patient. Acommunication link is used for transmitting the core body temperatureand the bodily activity level to an external monitor.

In another aspect of the invention, a method is provided for diagnosinga performance level of a heart in a patient. A core body temperature anda bodily activity level are determined. A relationship between the corebody temperature and the bodily activity level is also determined. Inresponse to determining that the relationship between the core bodytemperature and the bodily activity level is outside of a predeterminedacceptable relationship range, a first alarm message is generated.

In yet another aspect of the invention, an implantable heart monitor isprovided. The implantable heart monitor has a core body temperaturesensor for determining a core body temperature of a patient. A bodilyactivity sensor is used to determine a bodily activity level of apatient. The implantable heart monitor also has a transmission unit fortransmitting the core body temperature and the bodily activity level toan external monitor and a processing unit for calculating a relationshipbetween the core body temperature and the bodily activity level and forgenerating an alarm message in response to a determination that therelationship is outside of a predefined acceptable range. Thetransmission unit can transmit the alarm message to the externalmonitor.

The various aspects of the present invention may be more clearlyunderstood and appreciated from a review of the following detaileddescription of the disclosed embodiments and by reference to thedrawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting an exemplary relationship between observedcore body temperature measurements and heart rate measurements in normalpatients and in heart failure patients.

FIG. 2 is a block diagram depicting the blood system of a heart failurepatient with an implanted heart monitor that is an exemplary embodimentof the present invention.

FIG. 3 is a block diagram of a remote heart monitoring system that is anexemplary embodiment of the present invention.

FIG. 4 is a flow chart depicting an exemplary method for monitoring andreporting core body temperature and heart rate levels for a heartfailure patient.

DETAILED DESCRIPTION

In an exemplary embodiment of the present invention, an implanted heartmonitor includes sensors that measure various aspects of a heart failurepatient's heart. A remote heart monitoring system connects the implantedheart monitor to a care provider, such as a physician. The data providedby the implanted heart monitor permits the care provider to obtainvaluable data on the heart in order to make health care decisionsaffecting the heart failure patient's treatment. In many cases, themeasurement of core body temperature and other patient data will enablethe care provider to alter the patient's treatment to address thepatient's condition. The implanted heart monitor can communicate over awireless communication link with an external monitor. The implantedheart monitor may be implemented as part of a pacing device (i.e., pacemaker) or may be a separate unit devoted to monitoring functions. Theexternal monitor communicates with a monitoring station over acommunication link. The monitoring station can operate as a centralizeddata collection unit, collecting data from multiple external monitorsand multiple implanted heart monitors. Various other aspects of a heartfailure patient's heart and/or body can be monitored, such as heartrate, blood pH levels, blood CO₂ levels, and any other indications ofthe heart failure patient's activity. Various predetermined thresholdsmay be set to trigger alarms and/or data reports.

FIG. 1 is a graph depicting an exemplary relationship between observedcore body temperature measurements and heart rate measurements in normalpatients and in heart failure patients. The graph of FIG. 1 is atwo-dimensional graph with core body temperature levels indicated on they axis 100 in degrees Celsius and heart rate levels indicated on the xaxis 102 in beats per minute. The graph of FIG. 1 relates core bodytemperature measurements and heart rate temperature measurements fornormal patients along normal curve 104. The graph of FIG. 1 relates corebody temperature measurements and heart rate measurements for heartfailure patients along the heart failure patient curve 106.

As can be seen from the graph, in normal patients, core body temperatureincreases in approximately a direct relationship with an increase inheart rate. In heart failure patients, on the other hand, core bodytemperature stays constant or is reduced as the heart failure patient'sheart rate increases. As described above, this phenomenon has been welldocumented in medical literature. As mentioned above, recent researchascribes the drop in core body temperature to low blood pH levels. As aheart failure patient exercises, the heart failure patient experiencesan increase of CO₂ in its blood as the blood attempts to eliminate theCO₂ from the exercising muscles. The heart failure patient will normallyincrease its breathing volume in an attempt to evacuate the increasedlevel of CO₂ from the blood. However, in heart failure patients, theblood system cannot deliver the blood to the lungs fast enough tosupport an adequate CO₂ for O₂ exchange in the lungs. It is well knownthat higher levels of CO₂ correlate with lower levels of blood pH. AsCO₂ accumulates in the heart failure patient's body, the blood's pHlevel drops. Because pH is a catalyst for virtually every chemicalreaction in the body, the heart failure patient's chemical reactionswill be slowed by the reduced pH levels. As the blood's pH level dropswith the increased CO₂ levels, the heart failure patient's bodilychemical reactions responsible for heat production during exercise areslowed and the core body temperature stays flat or decreases.

In the graph of FIG. 1, a critical zone 108 has been defined. Althoughthe critical zone 108 could be tailored for any diagnostic and/ortreatment purposes, it represents the occurrence of a critical event inthe relationship between the core body temperature and the heart rate.In the case of FIG. 1, the negative slope of heart failure patient curve106 indicates that the core body temperature is dropping rapidly as thepatient's heart rate increases. By monitoring the slope of the heartfailure patient curve 106, a care provider (e.g., attending physician)could determine that a heart failure patient is experiencing adverseheart conditions. In response to this determination, the care providercould alter the patient's medical treatment or instruct the patient toseek medical attention. In the example of FIG. 1, heart rate is used asan indicator of a heart failure patient's bodily activity. Typically,increased bodily activity results in increased heart rate. However, asis well known in the art, a heart failure patient's heart rate canincrease for various reasons. Thus, monitoring heart rate alone is notnecessarily an indication that the heart failure patient is experiencingincreased bodily activity. Those skilled in the art will also appreciatethat other aspects of the heart failure patient's diagnostics can beused to indicate increased bodily activity. Such data may includebreathing volume, patient motion, and CO₂ levels.

Core body temperature is indicative of the temperature of bloodreturning to the heart from the rest of patient's body. Of course, corebody temperature can increase and decrease for various reasons.Consequently, the increase or decrease in core body temperature alone isnot necessarily indicative of an adverse heart condition. A concurrentdecrease in core body temperature and increase in patient bodilyactivity is indicative of an adverse heart condition. Consequently,exemplary embodiments of the present invention enable more effectivetreatment of a heart failure patient by monitoring the relationshipbetween core body temperature and heart rate (or other indications ofbodily activity).

FIG. 2 is a block diagram depicting the blood system of a heart failurepatient with a heart monitor that is an exemplary embodiment of thepresent invention. The typical heart 200 includes a right atrium 202, aleft atrium 204, a right ventricle 208, and a left ventricle 206. Theleft atrium 204 brings in arterialized blood from the lungs through thepulmonary veins 210. The pumping action of the heart 200 forces bloodfrom the left atrium 204 to the left ventricle 206 through a one-wayleft heart valve 212 in the direction of arrow A. The pumping action ofthe heart 200 forces blood from the left ventricle 206 through the aorta214 to the body's systemic circulation system 216. The systemiccirculation system 216 is a short-hand reference to the network of bloodvessels that distribute blood to all parts of the body. Blood isreturned to the heart 200 from the systemic circulation system 216through the venae cavae 218. The returning blood is characterized byhaving a higher CO₂ content. The blood transports oxygen to the systemiccirculation system 216 and eliminates CO₂ from the systemic circulationsystem.

Blood with high CO₂ content enters the right atrium 202 through thevenae cavae 218. The pumping action of the heart forces blood from theright atrium 202 to the right ventricle 208 through a one-way rightheart valve 220 in the direction of arrow B. The pumping action of theheart then forces the blood from the right ventricle 208 through thepulmonary artery 222 to the lungs 224. The blood is ultimately forcedinto capillaries in the lungs that expose the blood to air sacs. The airsacs of the lung 224 provide the architecture for exchanging CO₂ in theblood for oxygen in the lungs. Once the exchange has been made, theblood is forced from the lungs back into the heart 200 through thepulmonary veins 210.

Core body temperature is normally measured in the return path of theblood circulation system. Because all of the body's blood returnsthrough the venae cavae 218 to the right atrium 202, the blood enteringthe right atrium is referred to as the mixed venous blood pool. Notably,the blood in the venous blood pool has dissipated as much heat aspossible in the systemic circulation system 216 prior to re-entering theheart 200. A temperature sensor, such as a thermistor, can be placed inor near the right atrium 202 to measure the core body temperature in thevenous blood pool. In a one embodiment as shown in FIG. 2, a core bodytemperature sensor 226 is located inside the right atrium 202. Thoseskilled in the art will appreciate the core body temperature may bemeasured in various locations in addition to a location in the rightatrium 202. For example, measurements of skeletal muscle temperature,myocardial muscle temperature, or even skin temperature can be measuredand correlated to a corresponding core body temperature to determine themeasured core body temperature. In a practical application, a core bodytemperature sensor could be integrated into the outer casing of aconventional implanted pacing device. A temperature correlation tablecould be used to approximate the core body temperature, based on thetemperature detected at the pacing device casing.

The right atrium 202 includes a sino-atrial (SA) node 228. The SA node228 signals an electrical impulse to propagate through the heart 200 tocause the heart to beat. The SA node receives an electrical impulse fromthe nervous system and converts the electrical impulse to a heartbeat.An atrio-ventricular (AV) node 230 is a cluster of muscle cells locatedin the wall between the right atrium 202 and the left atrium 204. The AVnode 230 is part of the heart's 200 electrical system. The AV node 230helps deliver heartbeat signals from the atria to the ventricles. Heartrate measurements are often taken at the SA node 228, because the SAnode is the contact point from which the body's natural heart pacingsignals emanate. Even in heart failure patients, the SA node 228 willusually receive a detectable signal from the nervous system. The naturalheart-pacing signal can be detected by means of a heart rate sensinglead 232, attached to the heart 200 at the SA node 228.

The core body temperature sensor 226 and the heart rate sensor 232 canbe connected to an implanted monitor 234 by a core body temperaturesensing lead 236 and a heart rate sensing lead 238, respectively. Theimplanted monitor 234 can be an integrated component of a pacing deviceor may simply be an implanted monitor with no pacing functionality. Inan exemplary embodiment of the present invention, the implanted monitor234 can communicate with an external monitor (not shown) to communicatevarious data collected from the patient and/or analysis performed oncollected data. In any event, the implanted monitor 234 can measureheart rate and core body temperature data and can transmit that data toan external entity such as a care provider, an external monitor/alarmunit, or an external data collection center.

The implanted monitor 234 also can determine the relationship betweencollected data such as core body temperature and heart rate data. Forexample, the implanted monitor 234 could be used to calculate the slopeof a graph of the relationship between a heart failure patient's heartrate and core body temperature measurements. As described above, thedata collected and/or analyzed by the implanted monitor 234 may includevarious indications of bodily activity and/or heart performance.

FIG. 3 is a block diagram of a remote heart monitoring system 300 thatis an exemplary embodiment of the present invention. The remote heartmonitoring system 300 connects a heart monitor 302, implanted in a heartfailure patient 304, to a care provider (e.g., a physician), forexample, a physician at a hospital 306. The implanted heart monitor 302includes sensors that measure various aspects of the heart failurepatient's heart 308. The implanted heart monitor 302 can include aprocessing unit 303 for processing the measured data and for analyzingthe data to, for example, determine a relationship between the measureddata. In one example, the processing unit 303 is configured forcalculating or otherwise determining a relationship between blood pHlevel and bodily activity level. In a further example, the processingunit 303 is configured for generating an alarm message in response to adetermination that the relationship is outside of a predefinedacceptable range. The implanted heart monitor 302 communicates over awireless communication link 310 with an external monitor 312. Theimplanted heart monitor 302 may include a transmission unit 305 forcommunicating with the external monitor over the wireless communicationlink 310. In one example, the implanted heart monitor is operative totransmit the core body temperature and the bodily activity level to theexternal monitor, such as, for instance, a remote monitoring station.

The implanted heart monitor 302 may be implemented as part of a pacingdevice (i.e., pace maker) or may be a separate unit devoted tomonitoring bodily functions. The external monitor can be located withinthe heart failure patient's home 314 or may be mobile. Those skilled inthe art will appreciate that various implementations of the externalmonitor 312 are possible within the scope of the present invention. Itshould also be appreciated that the connection between the implantedheart monitor 302 and the external monitor 312 could be a hardwireconnection (i.e., not wireless), for example, when the remote heartmonitoring system 300 is used in a hospital room context.

The external monitor 312 communicates with a base station 314 over awireless communication link 316. Again, those of ordinary skilled in theart will appreciate that a hardwire connection could be used between theexternal monitor 312 and the base station 314. However, as with thewireless communication link 310 between the implanted heart monitor 302and the external monitor 312, the wireless communication link 316provides the most versatility and convenience to the patient.

The base station 314 is connected to a monitoring station 318 over acommunication link 320. The monitoring station can be used to collectdata from the implanted heart monitor 302, via the external monitor 312.Notably, the monitoring station 318 can collect data from multipleexternal monitors and multiple implanted heart monitors. That is, themonitoring station 318 can operate as a centralized data collectionunit. The monitoring station 318 can communicate with a hospital 306over a communication link 322. The monitoring station 318 cancommunicate with multiple hospitals and/or care providers to delivermonitored and/or stored data.

In the remote heart monitoring system 300 of FIG. 3, various aspects ofa heart failure patient's heart and/or body can be monitored. Forexample, the implanted heart monitor 302 may monitor core bodytemperature, ventilation rate, oxygen consumption rate, heart rate,blood pH levels, blood CO₂ levels, bodily movement, and any otherindication of the heart failure patient's bodily activity. In oneexample, a pH level sensor determines a core body temperature bydetermining a blood pH level and correlating a blood pH level into acore body temperature. In a further example, the implanted heart monitor302 is operatively connected to a blood pH level sensor and a bodilyactivity sensor and is configured to receive and process datarepresentative of the blood pH level and the bodily activity level. Inthis example, the implanted heart monitor 302 processes datarepresentative of blood pH level and correlates the blood pH data into acore body temperature. Various predetermined thresholds may be set totrigger alarms and/or data reports. For example, if the heart monitor302 determines that the measured core body temperature is outside apredefined acceptable range, the heart monitor may trigger an alarm.Alternatively, the heart monitor 302 may simply deliver the data to theexternal monitor 312.

The external monitor 312 may compare the measured levels topredetermined acceptable ranges and trigger alarms when a variance isdetected. Similarly, predetermined thresholds may be set for the heartfailure patient's heart rate and for the relationship between measuredindications. For example, an alarm may be triggered when the slope of agraph of core body temperature versus heart rate is too low.

While the remote heart monitoring system 300 of FIG. 3 has beendescribed in the context of monitoring the conditions of a heart failurepatient, it will be appreciated by those skilled in the art that theremote monitoring system could be implemented to monitor virtually anyaspect of a patient's health or activity.

The implanted heart monitor 302 periodically collects data and reportsthe collected data to the external monitor 312. The external monitor 312can process the data and relay the data to the monitoring station 318 atpredetermined intervals, via the base station 314. The external monitor312 may make a determination that the collected data indicates a changein patient wellness. In response to a determination that the patient'swellness has improved or declined, the external monitor 312 may generatea wellness report separate from the routinized collected data reporting.The external monitor 312 may determine that the collected data justifiesthe transmission of an alarm. In this case, the external monitor 312 cantransmit an alarm request to the monitoring station that can thengenerate an alarm and convey the alarm to the appropriate care providerat the hospital 306. Those skilled in the art will appreciate that thefunctionality of the implanted monitor and of the external monitor couldbe integrated into a single unit. It will also be appreciated that theimplanted monitor could detect and transmit virtually any heartcondition and/or body condition data.

The heart monitoring system 300 of FIG. 3 could be used in conjunctionwith a pacing device or any other heart failure treatment regimen. Whenthe implanted heart monitor 302 detects an out-of-range condition, analarm may be generated for the care provider, as described above. If,for example, the core body temperature measurement is outside of apredefined acceptable range, the care provider may access the patient'shistorical records to determine potential causes. The care provider alsomay cause the monitoring station 318 to initiate special communicationswith the external monitor 312 to gather more recent data on thepatient's heart or other diagnostic information. If the care providerreceives an alarm indicating a relationship between the core bodytemperature and the bodily activity level, the care provider may contactthe patient and urge the patient to seek immediate treatment. Of course,in a hospital context, the care provider may simply go to the patient'shospital room and attend to the patient.

Generally, a significant decrease in a heart failure patient's core bodytemperature without a coincident increase in bodily activity may signalan imminent heart failure episode, such as cardiac arrest. A decrease ina heart failure patient's core body temperature that is coincident withan increase in bodily activity is an expected relationship. However, ifthe decrease in core body temperature during increased bodily activityis too rapid, it too may signal an imminent heart failure episode, suchas cardiac arrest. In any event, the data provided by the implantedheart monitor permits the care provider to obtain valuable data on theheart in order to make health care decisions affecting the heart failurepatient's treatment. In many cases, the measurement of core bodytemperature and other patient data will enable the care provider toalter the patient's treatment to address the patient's condition (i.e.,make the patient's condition less pathological). This treatmentalteration may be as simple as alerting the patient to cease vigorousexercise, or as complex as modifying the operational parameters of thepatient's pacing device (i.e., pacemaker).

FIG. 4 is a flow chart depicting an exemplary method for monitoring andreporting core body temperature and heart rate levels for a heartfailure patient. The method of FIG. 4 begins at start block 400 andproceeds to step 402. At step 402, the heart performance and core bodytemperature of a heart failure patient is monitored. As described inconnection with FIG. 2, the step of monitoring heart performance may beperformed by an implanted heart monitor with a heart rate sensoroperative to detect a heart rate. The core body temperature monitoringmay be performed by and implanted heart monitor that uses a core bodytemperature sensor to determine the temperature of a venous blood pool.

The method proceeds from step 402 to decision block 404. At decisionblock 404, a determination is made as to whether the core bodytemperature is within a predetermined range. If the core bodytemperature is within the predetermined range, the method branches tostep 408. On the other hand, if the monitored core body temperature isnot within the predetermined range, the method branches to step 416through connector A. In the exemplary method of FIG. 4, thepredetermined range for core body temperatures may represent a range ofcore body temperature determined by a care provider to be a safe rangefor the patient. Those skilled in the art will appreciate that the rangemay differ from one heart failure patient to another and could,therefore, be configurable on a per-patient basis.

At step 416, an alarm message is generated to indicate that the measuredcore body temperature is outside of an acceptable range. The methodproceeds from step 416 to step 418, wherein the alarm message istransmitted to the care provider. Those skilled in the art willappreciate that a single alarm may be used for any out-of-rangecondition. Alternatively, a separate alarm may be used for each out ofrange condition. The alarm message may include an indication of themeasured data that has been determined to be out of the acceptablerange. The method proceeds from step 418 to step 420 and heartperformance and core body temperature monitoring is continued.

Returning now to decision block 404, if a determination is made that thecore body temperature is within the predefined range, the methodbranches from decision block 404 to step 408. At step 408, the core bodytemperature data is transmitted for storage. In the remote heartmonitoring system 300 of FIG. 3, the core body temperature data may bestored in the external monitor 312 for later transmission or may bestored in the monitoring station 318 in a centralized patient database.The method proceeds from step 408 to decision block 410.

At decision block 410, a determination is made as to whether the heartfailure patient's heart rate is within a predefined acceptable range. Ifthe patient's heart rate is outside of the acceptable range, the methodbranches to step 416, via connector A. The method proceeds from step 416to generate an alarm indicating the out-of-range condition, as describedabove. If, at decision block 410, a determination is made that the heartrate is within the predefined acceptable range, the method branches fromdecision block 410 to step 412.

At step 412, the heart rate data is sent for storage. As describedabove, the heart rate data may be stored in an external monitor, amonitoring station, or any other acceptable storage means for subsequentretrieval. A method proceeds from step 412 to decision block 414. Atdecision block 414, a determination is made as to whether the core bodytemperature versus heart rate slope is within a predefined acceptablerange. As described above in connection with FIG. 1, the relationshipbetween the core body temperature and the heart rate (or any otherindication of bodily activity) is a useful measurement for diagnosing aheart failure patient. If the slope is outside of the acceptable range,the method branches to step 416 and an alarm is generated as describedabove. If, on the other hand, the slope is within the range, the methodbranches from decision block 414 to step 402 and core body temperaturemonitoring is continued.

Although the present invention has been described in connection withvarious exemplary embodiments, those of ordinary skill in the art willunderstand that many modifications can be made thereto within the scopeof the claims that follow. Accordingly, it is not intended that thescope of the invention in any way be limited by the above description,but instead be determined entirely by reference to the claims thatfollow.

1. A heart monitoring apparatus, comprising: a CO₂ level sensorconfigured to determine a blood CO₂ level of a patient; a bodilyactivity sensor configured to determine a physical bodily activity levelof the patient; a processing unit configured to process datarepresentative of the CO₂ level and the physical bodily activity levelof the patient, the processing unit configured to use the datarepresentative of the blood CO₂ level and the physical bodily activitylevel to generate a diagnostic; and a transmission unit configured totransmit the data representative of the blood CO₂ level and the physicalbodily activity level to a monitor.
 2. The heart monitoring apparatus ofclaim 1, wherein the processing unit is configured to determine arelationship between the blood CO₂ level and the physical bodilyactivity level and to generate an alarm message in response to adetermination that the relationship is outside of a predefinedacceptable range.
 3. The heart monitoring apparatus of claim 2, whereinthe transmission unit is configured to transmit the alarm message to themonitor.
 4. The heart monitoring apparatus of claim 2, wherein the CO₂level sensor is configured to be implanted within the patient.
 5. Theheart monitoring apparatus of claim 4, wherein the bodily activity levelsensor is configured to be implanted within the patient.
 6. The heartmonitoring apparatus of claim 5, wherein the monitor is an externalmonitor that is configured to communicate the alarm message with anexternal remote monitoring station.
 7. The heart monitoring apparatus ofclaim 1, wherein the heart monitoring apparatus is configured tocorrelate the blood CO₂ level into a core body temperature of thepatient.
 8. The heart monitoring apparatus of claim 7, wherein thetransmission unit is configured to transmit data representative of thecore body temperature to the monitor.
 9. The heart monitoring apparatusof claim 1, wherein the monitor is configured to be implanted within thepatient.
 10. A method, comprising: determining a blood CO₂ level of apatient; determining a physical bodily activity level of the patient;using data representative of the blood CO₂ level and the physical bodilyactivity level to generate a diagnostic; and transmitting the datarepresentative of the blood CO₂ level and the physical bodily activitylevel to a monitor.
 11. The method of claim 10, comprising: determininga relationship between the blood CO₂ level and the physical bodilyactivity level; and generating an alarm message in response to adetermination that the relationship between the blood CO₂ level and thephysical bodily activity level is outside of a predefined acceptablerange.
 12. The method of claim 11, wherein determining the relationshipincludes processing data representative of the blood CO₂ level and thephysical bodily activity level of the patient.
 13. The method of claim11, comprising transmitting the alarm message to a monitor.
 14. Themethod of claim 11, comprising altering a patient treatment regimen inresponse to the determination that the relationship between the bloodCO₂ level and the physical bodily activity level is outside of thepredefined acceptable range.
 15. The method of claim 10, whereindetermining the physical bodily activity level includes determining aventilation rate of the patient.
 16. The method of claim 10, whereindetermining the physical bodily activity level includes determining anacceleration rate of the patient.
 17. The method of claim 10, comprisingtransmitting the data representative of the blood CO₂ level and thephysical bodily activity level to an external remote monitoring station.18. The method of claim 10, comprising correlating the blood CO₂ levelinto a core body temperature of the patient.
 19. An apparatus,comprising: means for determining a blood CO₂ level of a patient; meansfor determining a physical bodily activity level of the patient; meansfor using data representative of the blood CO₂ level and the physicalbodily activity level to generate a diagnostic; and means fortransmitting the data representative of the blood CO₂ level and thephysical bodily activity level to a monitor.
 20. The apparatus of claim19, comprising: means for determining a relationship between the bloodCO₂ level and the physical bodily activity level; and means forgenerating an alarm message in response to a determination that therelationship between the blood CO₂ level and the physical bodilyactivity level is outside of a predefined acceptable range.